C'mon. They're not going after him because he said or did anything that was remotely anti-Jewish or even pro-Nazi. It was a COSTUME party. He should have known the reaction, but that's what makes him stupid, not that he wore a stupid costume.
This is being done to teach Harry and his brother who the bitch is in the relationship between the British Media and the monarchy.
Your first paragraph makes no sense. If he didn't do anything which was perceived as anti-Jewish or pro-Nazi, then what is the action by Harry that requires his being taken to task? Your explanation is that he "should have known the reaction"; I have to ask "the reaction to what?"
Why is it stupid to wear a Nazi uniform to a costume party and why should anyone have a problem with it, even if the action is the action of a member of the royal family, if it isn't anti-semitic or pro-Nazi to do so? If your answer goes to perceptions you destroy your argument, because there has to be a perception of either stupidity or inflicted harm, negligence or something untoward in Harry's behavior in order to justify creating this kind of media firestorm in retribution for his actions. It isn't enough to say "he acted stupidly," because you have to answer the question "how so?" If you say "because he wore a Nazi uniform to a costume party and he should have known better," we're just travelling in circles.
Your second paragraph is so self-conciously flip I don't think it's penetrable, at least by me.